Adjustable pitch guide blades



Oct. 2, 1962 D. B. FOWERAKER 3,056,541

ADJUSTABLE PITCH GUIDE BLADES Filed March 25. 1959 2 Sheets-Sheet l Oct. 2, 1962 D. B. FOWERAKER 3,056,541

ADJUSTABLE PITCH cum: BLADES Filed March 23. 1959 2 Sheets-Sheet 2 Fatented Get. 2, 1962 This invention relates to adjustable pitch guide blades in axial flow rotary compressors. The invention is concerned with a linkage for connecting a ring of such guide blades for simultaneous pitch control.

The invention is particularly applicable to multi-stage,

axial flow rotary air compressors in gas turbine jet propulsion engines for aircraft. Such machines have been provided with adjustable pitch guide blades in order to permit them to operate more efiiciently over a wider range of rotational speeds. The adjustable guide blades may conveniently be mounted in bearings in the outer wall of the air intake passage feeding the compressor, and the linkages for connecting the guide blades may conveniently be located on the exterior of the outer wall and therefore outside the air intake and out of contact with the intake air flow. In that case the blade-connecting linkage will experience temperatures which may diller appreciably from those experienced at the same time by the outer wall of the air passage in which the guide blades are mounted, and should circumferential expansion or contraction of the outer wall occur so as to tend to create relative movement between the wall and the linkage, a cumulative interference with the selected pitch of the connected guide blades may result.

According to this invention there is provided an axial flow rotary compressor comprising a boundary wall for the working fluid, a ring of radially-extending guide blades each journaled in the boundary wall for rotation about a radially-extending axis to adjust the pitch thereof, the axes of rotation of the blades lying in a common radial plane, and the blades having respective actuating arms connected thereto and arranged substantially parallel to each other, each arm extending axially on each side of said plane, and a series of circumterentially extending links offset from but extending parallel to said plane, which links connect all the arms in train with each other, the arrangement being such that the arm of each blade is respectively connected to the arms of the two next adjacent blades by two of said links, which two links are disposed on opposite sides of the said plane, and means connected to one of the blades for holding it in selected angular positions about its axis.

In one form of the present invention the series of parallel-motion linkages has free ends in the sense that there is one pair of adjacent rocker arms which are not connected together by a link member, and in this case an actuating means for adjusting the blade pitch is preferably connected to one of the rocker arms at or near the middle of the series.

Alternatively however, if there is an even number of blades, the series may be endless in the sense that every pair of adjacent rocker arms is connected together by a link.

One embodiment of the invention will now be described by way of example and with reference to the accompanying drawings which show details of a multi-stage, axial flow, rotary gas compressor.

FIGURE 1 being a section along line l.1 of FIG- URE 2,

FIGURE 2 a plan view of an arcuate portion of an outer wall of an annular gas passage of FIGURE 1,

FIGURE 3 is a plan of a modified link for connection to actuator means,

FIGURE 4 a section of a rocker arm, the section being taken on line 44 of FIGURE 3,

FIGURE 5 shows the full circular arrangement of the guide blades, the number of blades being an odd number, and

FIGURE 6 shows the full circular arrangement Where the number of blades is even.

Referring to the drawings, the outer frusto-conical wall It of the annular intake passage of a multi-stage axial flow rotary gas compressor is provided with a ring of equally spaced apertures. These apertures receive recessed plates which are secured to the outer wall 16 by bolts 15. The plates 14- are centrally apertured to provide blade mountings for the blades 11 of a ring of guide blades, three of which are partially shown in FIGURE 1. The outer portions of each guide blade terminate in a hollow trunnion 25. This hollow trunnion 25 is surrounded by a sleeve 12 which is flanged at its innermost end. The flanged sleeve 12 is of increased outer diameter at its lower end near the flange to be received within the bushes 17. These bushes T7 are carried in the aperture of the recessed plate 14 and are of the same axial length as the part of the sleeve 12 of enlarged diameter. Surrounding the sleeve 12 at its smaller diameter part is the hub 13 of a rocker arm (13, 18a or 18b in FIGURES 2 and 3). The hub 13 is flanged at its lower end to bear on the step between the larger and smaller parts of the sleeve 12 and the bushes 17 are provided with flanges at each end which fit into the recessed plate which is shaped to prevent the bushes 17 moving towards one another. The flange at the lower end of the hub 13 bears also on the outer of the flanges of the bushes 17, and the flange of the sleeve 12 bears against the inner flange of the bushes 17. The hub 13, sleeve 12 and trunnion are provided with registering diametral holes through which a split tapered pin 16 is passed. The blades 11 are thus mounted for free rotation about the axis of the trunnion 25 but are held against axial movement by the mounting of the flanges as described.

Each rocker arm (18, 18a, 18b) normally extends transversely of the plane containing the pivot axes of the blades in the ring. Each double-ended rocker arm (18, 18b) has its hub approximately at its centre. The ends of the rocker arm are bifurcated and drilled to support a link pin 20. The link pin 20 is engaged by an eye bolt 21 which has a threaded shank 22. This shank 22 enters and engages the internally-threaded adjacent end of a connecting sleeve 23 to constitute therewith and with a shank 22 engaged with the other end of the connecting sleeve 23 a link member which extends parallel to the plane containing the pivot axes of the blades in the ring. The rocker arms 18 and the link members are so arranged that any one double-ended rocker arm 18 is connected to the adjacent two rocker arms respectively by a link member at each end, which link members lie in planes on opposite sides of the plane containing the axes of the blades in the ring. The link members and rocker arms thus constitute parallel motion linkages and together form a linkwork actuated by a pitch actuator as will hereinafter be described. In this embodiment there are an odd number of blades in the blade ring, two of the blades not being connected together by a link member, so that the system has two free ends. The rocker arms are all double-ended (as shown at 18) except for the rocker arms 18a connected to the two end blades, i.e. the blades which are not linked together. These rocker arms 18a are singleended as will be seen in FIGURE 2 where one is shown. The mid-blade of the blade ring i.e. the guide blade having an equal number of blades between it and the end blades on either side of it, is provided with a modified rocker arm 13b. This rocker arm 18b is provided with an additional arm 24 for connection to the pitch actuator. The arm 24 is bifurcated at its end for engagement by an eye bolt 21, the latter being screw threaded to a connecting sleeve 23 which is connected to the ram of an actuator for controlling the blade pitch. The actuator may be controlled in any desired manner, for instance it may be made responsive to the compressor r.p.m.

In operation, the actuator ram is moved to rock the modified rocker arm 18b. The resultant rocking movement is simultaneously transmitted by the open ended series of parallel motion linkages to the blades 11 on both sides of the modified rocker arm so as to cause them to pivot together about their respective pitch axes and to change their angle of pitch by the desired amount.

If the outer wall of the intake passage contracts or expands, the spacing between any two adjacent blades will vary and thus the spacing between the pivot axes of the rocker arms supported by these blades will also vary. If, however, the linkage is not similarly affected, as may well be the case because, for example, the inner surface of the outer wall but not the linkage is scrubbed by the intake flow of gas, the variation in spacing between three adjacent blades will be accommodated by a slight rocking movement of the rocker arm of the middle blade only, the orientation of the rocker arms of the blades on each side of it remaining unaffected. Thus a cumulative interference with the blade pitch is not permitted to build up. The rocker arms which will rock will be the arms spaced by an odd number of spaces from rocker arm 18b, i.e. the two arms adjacent rocker arm 18!) and each alternate rocker arm thereafter. When there is an even number of blades in the ring every pair of adjacent rocker arms may be connected together by a link.

Considering any group of three rockers, for example the three rockers shown in FIGURE 2, if the spacings x and y between the rocker axes are equal, then the lengths u and v of the arms of the middle rocker must be equal to ensure that, if the right hand side rocker is fixed and the distances at and y change equally, only the middle rocker turns around its axis. If however the spacings x and y are unequal, and change respectively by ax and ay (a being for example a coeificient of linear thermal expansion multiplied by a temperature difference), then for the left hand rocker to remain non rotated a(x+y) must be equal to (u-l-v) a0;

from which it follows that with u :0

The screw-threaded connection between the sleeve 23 and the eye bolts 21 permits manual adjustment of individual linkages.

I claim:

1. An axial flow rotary compressor comprising a boundary wall for the working fluid, a ring of radially-extending guide blades each journaled in the boundary wall for rotation about a radially-extending axis to adjust the pitch thereof, the axes of rotation of the blades lying in a common radial plane, and the blades having respective actuating anns connected thereto and arranged substantially parallel to each other, each arm extending axially on each side of said plane, and a series of circumferentially extending links offset from but extending parallel to said plane, which links connect all the arms in train with each other, the arrangement being such that the arm of each blade is respectively connected to the arms of the two next adjacent blades by two of said links, which two links are disposed on opposite sides of the said plane, and means connected to one of the blades for holding it in selected angular positions about its axis.

2. An axial flow rotary compressor as claimed in claim 1, wherein at least some of the links are adjustable in length.

3. An axial fiow rotary compressor comprising a boundary Wall for the working fluid, a ring of radially-extending guide blades each journaled in the boundary wall for rotation about a radially-extending axis to adjust the pitch thereof, the axes of rotation of the blades lying in a common radial plane, and the blades having respective actuating arms connected thereto and arranged substantially parallel to each other, each arm extending axially on each side of said plane, and a series of circumferentially extending links offset from but extending parallel to said plane, which links connect all the arms in train with each other, the arrangement being such that the arm of each blade is respectively connected to the arms of the two next adjacent blades by two of said links, which two links are disposed on opposite sides of the said plane, and means connected to one of the blades for holding it in selected angular positions about its axis, and wherein considering the blades in groups of three neighboring blades, the lengths of the two links connected to the arm which is connected to the middle blade of the group are x and y respectively, the distances from the axis of rotation of each blade to the points of connection to that blade of the two associated links are u and v respectively, and the values of u, v, x, and y satisfy the equation 4. An axial flow rotary compressor comprising a boundary wall for the working fluid, a ring of radially-extending guide blades each journaled in the boundary wall for rotation about a radially-extending axis to adjust the pitch thereof, the axes of rotation of the blades lying in a common radial plane, and two of said blades which are next adjacent each other having lever arms connected thereto which extend parallel to each other and transversely to said plane, and the two lever arms being free to any direct linkage between them, and the other blades having respective actuating arms connected thereto and arranged substantially parallel to the said lever arms, each actuating arm extending axially on each side of said plane, and a series of circumferentially extending links offset from but parallel to said plane which links connect all the arms, including the said lever arms, in train with each other, each of the actuating arms being respectively connected to the arms of the two next adjacent blades by two of said links, which two links are disposed on opposite sides of the said plane, and means connected to one of the blades for holding it in selected angular positions about its axis.

5. An axial flow rotary compressor as claimed in claim 3, comprising actuating means for adjusting the pitch of the blades, which actuating means is connected to one of the said arms on the opposite side of the ring of blades to the blades having said lever arms.

References Cited in the file of this patent UNITED STATES PATENTS 2,388,208 Foss Oct. 30, 1945 2,393,042 Hagen Jan. 15, 1946 2,435,092 Meyer Jan. 27, 1948 2,793,804 Woodbury May 28, 1957 2,857,092 Campbell Oct. 21, 1958 2,858,062 Allen Oct. 28, 1958 

